Heretofore, considerable efforts have been expended in developing and improving base wads for shotshells. The primary problem has been to incorporate within a single base wad all of the desired attributes thereof. A base wad must be adapted for interlock with the shotshell head, as by flowing into the rim portion thereof, for gas sealing purposes; as well as to provide a snug joint with the tube wall so that the force of the explosion, upon firing, will not be ineffectively dissipated. Additionally, it is of extreme criticality that a base wad be resistant to permanent deformation so that swelling, as it were, of the shotshell head is prevented for assuring ready ejectability or removal of the fired shotshell from the gun firing chamber. Base wads must necessarily embody appropriate elasticity so as to return to normal condition from any momentary distention or expansion upon firing. Furthermore, base wads must be dimensionally stable over long periods of time and without regard to the conditions of storage so that moisture gain or loss with attendant volumetric change does not occur to assure of optimum and consistent ballistic characteristics.
With the ever increasing demand for shotshells which are adapted for reloading by the individual shooter further requisites for base wads have become more evident, such as durability, so that the respective shotshell may be reloaded numerous times before there is any failure in the base wad. Also, economy is a serious factor.
The attempts to date to develop a base wad which contains the spectrum of desired properties have not been successful. In each instance at least one important deficiency has been present. Among such efforts has been the development of base wads of two-part construction embodying interlocking components; and the provision of base wad overlays, all of which prove most costly in production and of dubious gas sealing capabilities. Integrally formed wads have been primarily formed of convolute wound paper but the same frequently split upon firing which, understandably, brings about a swelling of the head for obstructing shell ejections. Furthermore, wads of cellulosic materials are subject to dimensional alteration by the absorption and loss of mositure through changes in ambient conditions. Base wads formed of plastic materials such as linear polyethylene have proved to be altogether too costly as well as extremely difficult in forming.
Another effort has been to mold a base wad from linear polyethylene and such is exemplified in the Comerford U.S. Pat. No. 3,269,311. Linear polyethylene is of high density and is relatively hard, being incapable of flowing sufficiently during the heading operation to properly lock into the head. Such linear polyethylene is too hard to retain a dish-shaped surface adjacent the propellant to provide an effective seal. If the heading pressure is increased to overcome this deficiency in flowability, the tube of the shell will be cut before arriving at a pressure high enough to reform such plastic. In view of the inherent resistance to reforming in the heading operation with resultant insufficient locking of such wads in the shell rim, the loss of the same from the shell after firing has been customarily encountered with such base wad remaining in the gun barrel and providing a condition where in the barrel may burst upon firing of the next shell. Accordingly, wads formed from linear polyethylene thus provide a very frightful hazard and because of their lack of capacity to reform, have not proved popular with the individual reloader.
Another prior art effort at developing a base wad is of the character shown in the Daubenspeck et al. U.S. Pat. No. 3,270,671 wherein the base wad is comprised of 30-60% of asbestos fibers and 70-40% of wood fibers, held together with a microcrystalline wax binder in a quantity equivalent to about 8% by weight of the asbestos wood fiber mixture. Wads of this particular type are not impervious to moisture and, hence, may absorb moisture from the powder or could, conversely, transfer absorbed moisture to the powder which in either case would have a severe and marked effect upon the ballistics. Furthermore, upon firing the temperatures developed are sufficient to effect some melting of the wax binder so that the outer surface of such base wads tends to fragment and become loose and thereby makes it extremely difficult, if not impossible, to reload the shell. An individual attempting to reload a base wad of the type now being discussed must use a hot spinning iron to repress the base wad before reloading to overcome the surface fragmentation. Also, it is evident that due to the moisture absorptive capacity of the base wads, the same are extremely sensitive to ambient conditions. It is evident that asbestos wood fiber base wads are not amenable to production by extrusion or injection molding but can only be formed by mechanical intermixing and subsequent compression.
Therefore, it is an object of the present invention to provide a base wad which may be most economically produced; which is readily formable so as to assure positive locking with the shotshell head; which is dimensionally stable, being resistant to moisture absorption or loss; which is highly durable; and which is resistant to failure so as to conduce to extensive reloadability of the associated shotshell.
It is another object of the present invention to provide a shotshell base wad which is constructed of a readily flowable, normally soft thermoplastic and mineral filler whereby the base wad is endowed with the elasticity and formability of the plastic together with the stability and strength contributed by the mineral.
It is a further object of the present invention to provide a base wad of the character stated which is amenable to high volume, rapid economic production by a variety of readily practiced methods.
It is a still further object of the present invention to provide a method for producing one-piece base wads of the present invention.
It is another object of the present invention to provide a base wad which is fireproof and thus being adapted for safe storage as well as conducing to non-hazardous reloading.